Objective: To compare the completion rate of hepatitis B vaccination among adolescents who receive primary care at 2 comprehensive high school-based health centers (SBHCs) and a hospital-based adolescent health center (AHC) to assess predictors for successful immunization. Methods: A retrospective chart review of patients seen for comprehensive history and physical examinations from September 1997 to March 1998 at 2 SBHCs and an AHC was conducted to determine the immunization status for hepatitis B. One SBHC (SBHC-A) had previously implemented an outreach strategy consisting of advertising through the school's loudspeaker, whereas the other SBHC (SBHC-B) and the AHC did not. Completion rates were assessed among all students requesting comprehensive history and physical examinations. A subset analysis among those without prior immunizations was performed. Results: Of 510 records reviewed, 406 had documented data for hepatitis B immunization status, and 191 (37 for SBHC-A, 59 for SBHC-B, 95 for AHC) did not have any prior hepatitis immunizations. The completion rate of hepatitis B vaccination was significantly higher at SBHC-A (76%) compared with the other 2 sites (29% for SBHC-B and 24% for AHC) (PϽ.001). Conclusion: Patients with access to SBHC services that strongly emphasize outreach were more likely to complete the hepatitis B vaccination series.